A speedboat moves at a rate of 21 km/hr in still water. How long will it take someone to ride the boat 60 km downstream if the river's current moves at a rate of 9 km/hr?
To answer this question, we need to consider the speed of the boat relative to the water and the direction of the current.
Let's break down the problem. The speedboat is traveling downstream, which means it is moving in the same direction as the river's current. In this case, the speed of the boat relative to the water is the sum of the boat's speed in still water (also known as its speed over ground) and the speed of the current.
Given:
- Speed of the boat in still water: 21 km/hr
- Speed of the river's current: 9 km/hr
- Distance to be covered downstream: 60 km
To find the time it will take to ride the boat downstream, we can use the formula:
Time = Distance / Speed
Here, the distance is 60 km and the speed is the combined speed of the boat and the current.
The speed of the boat relative to the water is the sum of the boat's speed in still water and the speed of the current:
Speed = Boat's speed in still water + Current's speed
So, the speed is: 21 km/hr + 9 km/hr.
Substituting the values:
Speed = 30 km/hr
Now, let's calculate the time:
Time = Distance / Speed
Time = 60 km / 30 km/hr
Time = 2 hours
Therefore, it will take 2 hours for someone to ride the boat 60 km downstream.